1. Field of the Invention
This invention relates in general to offshore drilling for oil and gas, and in particular to a system for tensioning a section of casing extending between a subsea location at the sea floor and a surface wellhead located on a platform at the surface.
2. Summary of the Prior Art
In one type of offshore drilling and completion, the wellhead housing or casing head will be located at the surface on a platform. Lower strings of casing in the well are supported on the subsea floor by a mudline hanger or subsea housing. Subsequently upper strings of casing will be installed to extend from the subsea location to the surface platform. Tension needs to be applied to the upper strings of casing, as well as adjustment made for height differences.
Systems are known for adjusting the length of the upper strings of casing and applying tension to the casing above a subsea location. These systems employ a variety of adjustable load shoulders, including rings mounted to the casing which operate with rotation, rings that mount to the casing and adjust by ratcheting, and others that axially move the casing head shoulder.